Broadcast and multicast communications are a form of point-to-multipoint communications wherein information is simultaneously transmitted from a single source to multiple destinations. The third generation partnership project (“3GPP”) long term evolution (“LTE”) describes an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communications to cope with continuing new requirements and a growing base of users. The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards. The 3GPP LTE work item should result in new recommendations for standards for the UMTS.
One of the areas being considered in the LTE is the concept of uplink transmissions. Uplink transmissions are the transmissions that occur between the user equipment (“UE”) and the evolved base station (which may be referred to interchangeably as “e-Node B” or “eNB”). In order to provide high spectral efficiency of the LTE, it is the current working assumption that hybrid automatic repeat request (“H-ARQ”) will be utilized along with mechanisms such as fast or semi-fast link adaptation (adaptive modulation and coding), as well as, potentially, some kind of power control. H-ARQ is an error correction/control measure that automatically requests retransmission of data packets when an uncorrectable error is detected in a data packet.
Typically, prior to transmission, the data block and any error-detection information, such as cyclic redundancy checks (“CRC”), are encoded with an error-correction code, such as a Reed-Solomon code or Turbo code. When the coded data block is received, the receiver usually first decodes using the error-correction code. When the error-correction code is not capable of correcting all errors, the receiver requests retransmission of the data packet.
When looking at an implementation of H-ARQ in the uplink data channel, however, there is also a desire to have some feedback to be able to control the H-ARQ process (e.g., acknowledge (“ACK”) or negative ACK (“NACK”) to tell whether the data packet was received correctly at the e-Node B). One of the concerns for the LTE is how to optimize the utilization of the resources available on the physical air interface in such a way that produces a high performance result, while reducing the amount of resources used for control signalling. For the LTE uplink H-ARQ, it has been decided that the H-ARQ operation should be based on synchronous processes, such as when a retransmission of an erroneously received data packet would routinely occur at a pre-determined time instant after the initial transmission (delayed by ‘n’ transmission time intervals (“TTIs”)). The adaptive and non-adaptive H-ARQ options are supported by the third generation partnership project.
Non-adaptive H-ARQ uses the same physical resources that were used for the initial transmission for the retransmission, while adaptive H-ARQ obtains a new resource assignment to select which of the new resources to use for the retransmission. Since the adaptive H-ARQ allocates new physical channel resources for retransmissions, it accommodates potential frequency and interference diversity, which helps avoid data collisions through user equipment movement. One problem with adaptive H-ARQ, however, is that each retransmission will use a full entry in the resource allocation information.
Non-adaptive H-ARQ requires only a small amount of signaling. In extreme cases, only a single bit is used to request the retransmission, since both UE and e-Node Bs already generally know what to do for a retransmission. That is, both the UE and e-Node Bs are pre-configured with the information regarding which physical resources are allocated/reserved for the retransmission. Since the retransmission happens in a pre-defined place in the resource domain, however, there is generally no frequency or interference diversity. This lack of diversity allows occasional packet collisions due to the use of resources that may have already been allocated to semi-permanent users. Thus, each of the currently available H-ARQ schemes includes problems along with their respective benefits.
Accordingly, what is need in the art is a system and method that effectively manages a request for and the retransmission of data that overcomes the deficiencies in the prior art.